Re: some grammar fixes for docs

Michael Paquier <michael(at)paquier(dot)xyz> writes:
> On Thu, May 16, 2019 at 05:11:37PM +0300, Liudmila Mantrova wrote:
>> - Transaction which last more than <replaceable>limit</replaceable> milliseconds
>> + Transactions that last more than <replaceable>limit</replaceable> milliseconds

> I don't see much of a difference between "which" or "that" in this
> context, and you are right about the plural for "Transactions". Any
> native English speaker around or anybody with an extra opinion?

A lot of native speakers are sloppy about this :-(, but Liudmila is
correct.

Grammarians will tell you that "which" after a noun introduces a
descriptive clause (something that just adds information about an
already sufficiently-defined subject) while "that" introduces a
restrictive clause (something that narrows the scope of the subject).
So,

Transactions that have property X have property Y.

is just asserting "if X then Y"; it makes no claims about transactions
that do not have property X. But

Transactions, which have property X, have property Y.

is basically asserting that all transactions have both properties.
(Adding or removing the commas doesn't change the meaning, but it's
often easier to read it correctly with the commas. Or you could use
parentheses for the same effect. Using commas/parens in this way
with "that" is incorrect, mainly because it makes the reader wonder
if you meant "which" instead.)

This distinction is widely ignored in casual speech or writing, but
it's still recognized in formal writing. I think our manual is
formal enough that we should try to get it right.

regards, tom lane